Sara Barron is an area nurse in the region and was the first to report cases of anencephaly, or babies born with much of their brain and skull missing.

"I was just stunned. Three in a couple month period of time. That's unheard of. And they're such tragic terrible outcomes," said Barron.

Barron's shocking discovery prompted an investigation by the state health department, which showed that in three counties, in a three year period, there were 23 cases of anencephaly, which is a rate four times the national average.

But what could be causing such a high rate in Yakima Valley? Is it just a coincidence, or something more serious?

Epidemiologist Mandy Stahre at the Washington State Health Department conducted the investigation.

Reporter: "Did you find an answer?"

"We have not found an answer, and that's the very frustrating part," said Stahre.

But Sara Barron wonders if perhaps they didn't find anything because they didn't look hard enough. For starters, the state hasn't spoken to any of the families who had the babies with birth defects. Not a single one. They haven't asked key questions like what they ate, or if they'd been exposed to pesticides sprayed in this agricultural area, and that outrages Andrea Jackman, whose daughter, Olivia, was born with spina bifida, another type of neural tube defect.

Reporter: "So when this happens they wonder gee did the moms all have similar occupations, or did they have similar diets, has anyone called you to ask you these questions?"

"Nobody's asked me anything," said Jackman.

So if they didn't talk to moms like Jackman, how did the state do its investigation?

"We looked at all the information that was included in their medical records," said Stahre.

For example, what prescription drugs they were taking, and if they had an underlying condition such as diabetes, but medical records don't have details about diet or pesticide exposure, two key considerations for this type of birth defect.

In their own press release, the Washington State Health Department says, "Medical record reviews might not have captured all information, preventing a cause from being identified."

Reporter: "Medical records don't tell you everything."

"No, they don't," said Stahre.

Reporter: "So if medical record don't answer everything why not just get on the phone and talk to these women?"

"Well, we have to weigh that heavily. This is a devastating diagnosis. And we know that for a lot of these women they had to make some hard choices. We have to weigh how invasive we want to be with these types of interviews," said Stahre.

Jackman says that attitude is condescending and paternalistic to moms like her, and harmful. She wants state investigators to ask her questions. After all, her answers could help solve the mystery and prevent more tragedies.

"If anything, will help another mom to not have to go through what I went through, I would be fine with it. What are you researching if you haven't physically called the families to find out? What are you researching?" said Jackman.

Reporter: "Has the state done enough to try to figure out what the answer is?"

"I don't believe so," said Jackman.

In her mind, there's no way a four-fold increase in the birth defect rate could be by chance.

"If it just happened to one person it could be random, but the fact that there's so many different people that it's happened to, there's gotta be something that you can pinpoint that caused this," said Jackman.

Stahre, the state epidemiologist, says the investigation is continuing and they may interview moms like Jackman at some point.

Reporter: "As time passes and you call these women years after their children were born, won't memories start to fade?

"It's very possible," said Stahre.

Reporter: "For a woman who might be pregnant now, should they be worried?"

"I don't think so," said Stahre.

But nurse Sara Barron isn't so sure.

"I think it's very scary. I think that there's absolutely something going on that needs to be investigated more thoroughly," said Barron.

And Olivia's mother isn't so sure either.

"There's gotta be something. It could even be the smallest thing. Not knowing is scary," said Jackman.